Warning devices that are triggered or turned on by more rapid than normal deceleration of a vehicle are disclosed in U.S. Pat. Nos. 3,559,164 issued Jan. 26, 1971, to Bancroft et al., for VEHICULAR DECELERATION SAFETY CIRCUIT MEANS; 3,760,353 issued Sep. 18, 1973, to Hassinger for EMERGENCY VEHICULAR WARNING SYSTEM; 3,846,749 issued Nov. 5, 1974, to Curry for VEHICLE BRAKE LIGHT CONTROL SYSTEM; 4,258,353 issued Mar. 24, 1981, to Carlson for VEHICLE ACCELERATION/DECELERATION WARNING SYSTEM; and 4,357,594 issued Nov. 2, 1982, to Ehrlich et al. for VEHICULAR HAZARD WARNING SYSTEM.
The Bancroft system has the disadvantage that it is not a self-contained unit but is instead designed to be incorporated in the brake light circuit of the vehicle in which it is installed. This can be a comparatively difficult matter.
In addition, the deceleration sensing component of the Bancroft et al. device is a pendulum which is exposed and therefore subject to damage and misalignment. Furthermore, that pendulum operates an also exposed microswitch which is subject to wear and to damage by the fine, erosive particles stirred up by a moving vehicle.
Another disadvantage of the Bancroft et al. arrangement is that visual warning of vehicular deceleration is given by turning a conventional incandescent bulb on and off. This can only be done at a comparatively slow rate. Consequently, the visual warning display may not make it obvious to an observer that a dangerous situation exists.
Still another significant disadvantage of the Bancroft et al. device is that the pendulum which triggers the device is so designed and oriented that a mere sharp bump in a road, for example, could displace that pendulum enough to close the associated microswitch and turn the visual warning display on. This would be annoying to the driver of a following vehicle, at best. More likely, this would create a danger by falsely indicating that a panic stop was being made.
Still another disadvantage of the Bancroft et al. device is that the visual warning display remains on only so long as deceleration is severe enough to effect a microswitch-closing displacement of the switch-operating pendulum. Consequently, in the event of a short, but severe, deceleration, the visual warning display might not be on long enough to clearly indicate to an observer that a panic stop was being made.
Finally, there is no provision for manually operating the visual warning display of the Bancroft et al. device. This is a disadvantage because there are many situations not involving panic stops, such as a stalled vehicle, in which a visual warning display can also be employed to advantage.
Like that disclosed by Bancroft et al., the Hassinger system employs a visual warning display with conventional incandescent filaments. The Hassinger device may, therefore, likewise not prove capable of being turned on and off fast enough to provide a clear warning of a present danger.
Another disadvantage of the Hassinger system is that the control circuit for its visual warning display is enabled by a mercury switch. Switches of that type have the disadvantage in vehicular applications that the mercury tends to break up when the vehicle goes over a hard bump, for example, or is subjected to vibration on a dirt or other rough road. Once this occurs, the switch may stay on when it should turn off. Conversely, it may thereafter not come on when it should.
In addition, the Hassinger unit is designed to be mounted under the dash of the vehicle in which it is installed. This area is notoriously difficult to reach in a modern automobile. It would accordingly be difficult and expensive to install the Hassinger system in such a vehicle.
Furthermore, the Hassinger unit must be manually reset. This is a significant disadvantage because the device will be inoperative in a subsequent dangerous situation if the vehicle operator forgets to reset it.
In addition, the Hassinger device has a number of mechanical parts including pins, springs, adjustment screws, etc. These are subject to partial or total failure. In addition, it would be difficult and burdensome to make those adjustments after installation which are required for the Hassinger device to operate properly. Finally, like Bancroft et al., Hassinger makes no provision for manually operating the visual warning display of his device in circumstances which pose a danger but do not involve abnormal deceleration.
Carlson discloses yet another device which has the drawback that its visual warning display has an incandescent filament.
Also, the Carlson device is quite complicated and requires special wiring. Consequently, an actual unit of the character proposed by Carlson would be expensive to produce and install. And its complexity would make it less than optimally reliable.
Furthermore, the Carlson device is yet another one which must be manually reset. In his case, however, the situation is exacerbated because the visual warning display will continue to operate until the decelerometer is manually reset. Consequently, the visual warning display continues to flash, perhaps indicating that an emergency situation exists, long after the emergency has ended. This is particularly important because the driver of the vehicle may not be aware that the device is continuing to operate.
Yet another disadvantage of the Carlson system is that it employs a trigger relay to control the operation of the visual warning display. This is a drawback because relays of that character are unreliable when used in vehicles in which they are subject to shock and vibration.
The Curry device is yet another one which employs the brake lights of the vehicle in which it is installed to provide a visual display warning. Consequently, the Curry device has the same disadvantages as other warning devices employing that scheme.
Also, at least in part, the deceleration indicative input of the Curry device is taken from the speedometer cable of the vehicle in which the device is installed. This arrangement has the disadvantage that it is not capable of taking into account the nature of the terrain on which the vehicle equipped with the device is operating. For example, a much lower rate of deceleration is required to send a vehicle descending a steep hill into a skid than is necessary to cause that vehicle to skid while ascending the same hill. The speedometer cable-derived input of the Curry device is not capable of so altering the operation of that device's display-controlling circuitry to take factors such as the one just identified into account.
Furthermore, the Curry device employs extensive wiring and several pick-ups. As a practical matter, it could therefore only be installed in a vehicle while that vehicle was being manufactured. Thus, the Curry device has the disadvantage that it probably would not be practical to install in an already manufactured vehicle even at the dealer level.
An extremely complicated vehicular warning device is disclosed in the Ehrlich et al. patent. That device has a large number of mechanical components including four sensors, mechanical clutches, etc. As a result, the Ehrlich et al. device would be expensive to manufacture and to maintain. It would be less than optimally reliable because of the failure susceptibility of its many mechanical components.
In fact, the Ehrlich et al. device is so complicated that it requires extensive adjustments after the device is installed. This could make installation impractically expensive by placing it beyond the reach of the average vehicle owner.
Furthermore, the Ehrlich et al. device would necessarily have a relatively slow response time: (1) because of the above-mentioned mechanical components, and (2) because the turning on of the visual warning display is controlled by a relatively slow acting, mechanical relay.
In addition, the Ehrlich et al. device is yet another one which utilizes a visual warning display with an incandescent filament. It, too, has the above-discussed disadvantages appurtenant to that type of display.
Yet another disadvantage shared in common by those above-discussed systems employing low mounted, dual vehicular brake lights as a visual warning display is that an observer able to see the light at only one side of a vehicle may mistakenly take the flashing display for a turn signal rather than a warning of a present danger.